Toby Fox built Undertale almost alone. He wrote the script, composed the music and designed the game, with artwork and character designs from Temmie Chang and a few guest designers. It came out for OS X and Windows in September 2015, then reached Linux in 2016, PlayStation 4 and PlayStation Vita in 2017, the Nintendo Switch in 2018 and Xbox One in 2021, with a PC (Microsoft Windows) release among the platforms it shipped on. It holds a 9.6 out of 10 across 13 outlets in the IGDB critic aggregate, and it has sold at least five million copies.
Trailer, via PlayStation.
A Child Falls Into Mount Ebott
Undertale opens on a war. Humans and monsters once ruled the Earth together, the game’s opening text says, until a terrible war broke out between the two races. The humans won, and sealed the monsters underground with a magical spell.
In the year 201X, a small child climbs Mount Ebott. People say those who climb it never return. The child enters a cave to escape the rain, finds an enormous hole, leans in for a better look, and falls.
That is the whole setup, and the game spends the rest of its run testing what you do with it. The Underground is a large, secluded region beneath the surface, cut off by a magical barrier with a single gap at the mountain. The child wants back out. The monsters in the way have their own history with humans, and most of them would rather not let another one leave.
Flowey, Toriel and the Lie About LOVE
The first monster the child meets is Flowey, a sentient flower who explains the game’s mechanics and lies about “LV,” or “LOVE,” in an attempt to kill them. Toriel, a motherly goat-like monster, rescues the child and teaches them how to get through conflict without killing. She wants to adopt the child and keep them away from Asgore, the king of the Underground.
The child leaves her anyway, heading for Asgore’s castle and the barrier inside it. Along the way come the skeleton brothers Sans and Papyrus, who serve as sentries for the Snowdin forest; Undyne, head of the royal guard; Alphys, the kingdom’s royal scientist; and Mettaton, a robotic television host Alphys built.
The backstory lands later. Asriel, the son of Asgore and Toriel, once befriended the first human to fall into the Underground. When that child died suddenly, Asriel used the soul to cross the barrier and carry the body home. Humans on the surface attacked and killed him. Asgore declared war. By the present day he has collected six human souls and needs one more to break the barrier.
A Heart in a Bullet Hell
Combat is where Undertale stops behaving like a normal role-playing game. Fights run turn-based, but the player’s turn is a small heart representing the soul, steered through attacks from the opposing monster in the style of a bullet hell shooter. Later fights add colored obstacles, and boss battles change how the heart moves.
You can attack, with timed button presses. You can use the ACT option to check an enemy’s attacking and defending attributes or to do something specific to that enemy. Kill a monster and you earn EXP, which raises your LOVE, plus gold. Find the right responses, or hit an enemy down to low HP without finishing it, and you can spare it and walk away.
Some boss fights only end peacefully if you survive long enough for the other character to finish talking. That is the design in one line: the game treats patience as a mechanic.
Two Ways Through the Same Story
The choices carry. Dialogue, characters and story shift with the outcomes, and the game runs multiple branches and endings. The player’s morality is the cornerstone the whole thing was built on.
| Spare route | Kill route | |
|---|---|---|
| What you do | Use ACT, find the right responses, or leave enemies at low HP | Attack with timed presses until the enemy dies |
| What you get | Befriended monsters, alternate dialogue, a different story | EXP, higher LOVE, gold |
| How fights end | Some bosses require surviving until their dialogue finishes | The fight ends when the monster is dead |
Neither column is the “real” game. Undertale built its plot around the fact that you can see both.
Where the Inspiration Shows
Fox has been open about his sources: the Brandish, Mario & Luigi and Mother role-playing series, the Touhou Project bullet hell shooters, and Moon: Remix RPG Adventure. Undertale was originally set for mid-2014 and slipped.
The delays did not cost it. The game drew acclaim for its thematic material, combat system, musical score, originality, story, dialogue and characters. Reaction to the art style was mixed, and that is the fair knock — the sprites are plain next to everything else on offer. The soundtrack is not.
What holds up is the argument Undertale makes about players. Most role-playing games hand you a sword and call killing progress. Undertale hands you the same sword and then lets you put it down, and it remembers when you do not. Flowey’s lie about LOVE is the thesis: the stat you grind is not affection, it is the capacity to hurt things.
The writing is funnier than its reputation suggests, and the horror lands because the comedy came first. Sans and Papyrus are a comedy duo until they are not. Mettaton is a television host until he is a fight. Alphys is a scientist with a lab full of things she would rather not explain.
The bullet hell heart is the smartest piece of the design. It turns every enemy’s personality into a pattern you have to read, so a monster’s character is something you learn with your hands rather than read in a menu.
Undertale is not flawless. The art style is the weakest part of the package, and the game leans on writing and music to carry scenes that a bigger budget would have staged.
None of that dents the verdict. Undertale is the rare game whose mechanics and themes are the same thing, made by one person who wrote the script and the score himself, and it has sold at least five million copies. The comparison that matters is not Undertale against its influences. It is Undertale against every other game that gives you a kill button and never asks why you pressed it.
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